1. Field of the Invention
The present invention relates to a glass body with a porous coating and method for making it as well as a solution for making the porous coating.
2. Description of the Related Art
EP 0 897 898 A2 describes a method for depositing an optical coating on a flat glass plate composed of soda lime glass by means of a sol or sol mixture.
In U.S. Pat. No. A 2,601,123 a method of making a porous SiO2 coating on glass is described. This sol gel coating method based on the use of a sol with a highly dispersed SiO2 particles comprises a simple dipping step that provides a porous SiO2 coating on soda lime glass.
DE 199 18 811 A1 discloses a process, in which a standard pre-stressed safety glass, also a soda lime glass, is provided with a porous SiO2 coating.
Also DE 196 42 419 A1 and DE 100 18 697 A1 describe methods for making porous coatings.
A typical composition of soda lime glass, in percent by weight on an oxide basis, is 72%, SiO2; 14%, Na2O(+K2O); 9%, CaO; 3to 4%, MgO; and 1%, Al2O3.
DE 1 941 191 describes a process for making transparent, glassy, crystalline or glassy-crystalline inorganic multi-component materials, preferably in thin layers. Above all, sensitive glasses that can be attacked, for example, by water should be protected with these layers.
K. Cathro, D. Constable u. T. Solaga, state that porous SiO2 coatings adhere only poorly to borosilicate glass in Solar Energy 32 [5], p. 573 (1984). A modification of this method which is especially applicable to PYREX® is suggested, in which an after-treatment step in which the glass is immersed in a sodium bicarbonate (NaHCO3) solution is required. Because of that this method is expensive and extensive. Furthermore accelerated aging takes place because of Na2CO3 particles in the coating surface, which leads to a reduction of the transmission, as described by Helsch, Journal of Non-Crystalline Solids, 265, pp. 193 to 197 (2000).
The poor adherence of porous SiO2 coatings is also a problem for other chemically resistant glasses, with alkali-poor or alkali-free glasses, for example, silica glass.